A grid of power lines typically distributes electricity. These power lines spread out from a main generator station and convey the electricity to numerous substations. The voltage of this electricity is stepped up for efficient conducting of electric power. Each substation contains one or more power transformers that are used to step down the voltage to lower levels for subsequent conducting through a distribution network. The distribution network has numerous smaller distribution transformers, which lower the voltage of the electricity conveyed to households or other end users. Conventionally, the input voltage is called the primary voltage and the output voltage is called the secondary voltage.
Transformers are well known and normally include a transformer core and winding subassembly placed in a housing. A typical housing includes a tank containing transformer fluid (e.g., mineral oil) which electrically insulates and absorbs heat from the immersed transformer core and winding subassembly. Vanes attached to the tank transfer such heat to the atmosphere, with such heat transfer usually aided by cooling fans blowing against the vanes. There may be various cooling stages (e.g., stage 2-50% of pumps and fans; stage 3-100% of pumps and fans).
Online transformer monitoring systems are known for monitoring transformer operations to detect malfunctions. Existing online transformer monitoring systems are based on directly comparing measured quantities to threshold values (constants). While this allows power producers and distributors to ascertain when certain measured quantities fall outside the threshold values, this approach generates a relatively large number of false alarms of transformer malfunction.